<template>
	 <div class="list">
	 	 <ul class="item">
	 	 	<li 
	 	 	   class="item" 
	 	 	   v-for="item of letters" 
	 	 	   :key="item" 
	 	 	   :ref="item"
	 	 	   @touchstart="handleTouchStart" 
	 	 	   @touchmove="handleTouchMove" 
	 	 	   @touchend="handleTouchEnd"
	 	 	   @click="handleLetterClick">
	 	 		{{item}}
	 	 	</li>
	 	 </ul>
	 </div>
</template>

<script>
export default {
	name: 'CityAlphabet',
	props: {
		cities: Object
	},
	computed: {
        letters () {
        	const letters = []
        	for(let i in this.cities){
        		letters.push(i)
        	}
        	return letters
        }
	},
	data () {
		return {
           touchStatus : false,
           startY: 0,
           timer: null
		}
	},
	updated () {
        this.startY = this.$refs['A'][0].offsetTop
	},
	methods: {
		handleLetterClick (e) {
			this.$emit('change',e.target.innerText)
		},
		handleTouchStart () {
            this.touchStatus = true
		},
		handleTouchMove (e) {
           if (this.touchStatus) {
           	   if (this.timer) {
           	   	  clearTimeout(this.timer)
           	   }
           	   this.timer = setTimeout(() => {
                   const touchY = e.touches[0].clientY -79
                   const index = Math.floor((touchY - this.startY) / 20)
	               if (index >= 0 && index < this.letters.length) {
	               	   this.$emit('change',this.letters[index])
	                }
           	 },16) 
           }
		},
		handleTouchEnd () {
           this.touchStatus = false
		}
	}
}
</script>

<style lang="stylus" scoped>
   @import '~styles/varibles.styl'
	.list
	   display: flex
	   flex-diretion: column
	   justify-content: center
	   position: absolute
	   top: 4.58rem
	   right: 0
	   bottom: 0
	   width: .4rem
	   .item
	      line-height: .4rem
	      text-align: center
	      color: $bgColor
</style>